Outer-sphere interactions

Outer-sphere interaction in aqueous solutions of complex compounds. V. E. Mironov, Russ. Chem. Rev. (Engl. Transl), 1966,35, 455-469 (123). 

In studies on solvent effects involving variation in the composition of two component mixtures, similar types of outer-sphere interactions yield preferential solvation wherein the solvent composition of the outer-sphere may differ markedly from the bulk solvent composition. Supporting electrolyte species and buffer components may also participate in outer-sphere interactions thereby changing the apparent nature (charge, bulk, lability) of the reacting solvated metal ion or metal complex as perceived by a reacting ligand in the bulk solvent. 

Types of metal adsorption to mineral and organic surfaces (a) outer sphere interactions, (b) adsorption by electron-donor groups, (c) adsorption by negatively charged surface sites, and (d) adsorption to surface groups capable of forming metal-covalent bonds. The only parts of the molecular structure of the particle shown are the atoms engaged in metal adsorption. 

FIGURE 4. Typical outer-sphere interaction of [Mg(H20)5] with two GC base pairs in the major groove of a DNA double helix... 

Each of the species mentioned above can be expected to exhibit different interactions with Mg + and the binding situation is even more complex than with carboxylates. In addition to outer-sphere interactions, phosphates, like carboxylates, are capable of... 

When metal cations are placed in aqueous solutions two kinds of spheres normally appear (a) a sphere of water molecules that binds directly to the metal, called inner coordination sphere (or simply, inner sphere), and (b) a more loosely bound group of water molecules (not directly bound to the metal), called outer coordination sphere (or simply, outer sphere). In this way, a cationic complex can have an outer sphere interaction with an ionic ligand or a solvent molecule without displacing the inner ligands directly bonded to the metal. At higher anion concentrations, the outer sphere complex [M(H20)6]n+An is more prevalent than its corresponding inner sphere complex, [M(H20)5A], Interestingly, the number of inner-... 

To rationalize the observed trends in the values of c, as defined here, it is necessary to propose that the dominant outer-sphere interactions are the Cr(OH2)6-n(OS(CH3)2)n3+ system, a hydrogen bonding interaction between solvent dimethyl sulfoxide and coordinated water... 

Interestingly, specific M +-nucleic acid interactions determined in solution for the hairpin ribozyme by spectroscopic and chemical interference methods were not later found in their X-ray crystal stmctures. Even more confusing were results of X-ray crystallography " and initial solution experiments, which both determined up to two, presumably functionally important Mg + ions in the catalytic center of the hammerhead ribozyme. However, as demonstrated recently in biochemical experiments in solution, neither of these ribozymes require either inner- or outer-sphere interactions with particular metal ions for catalysis. ... 

Typical examples of the mixed outer-sphere interactions are present in the crystal structure of yeast tRNA . In contrast to a number of outer-sphere H-bonds between the metal-coordinated ligands and tRNA residues, these site-specific complexes contain only a few direct, inner-sphere bonds either to phosphate alone (Mg +), to phosphate and bases (Mn +), or to guanine alone (Pt +) (Figme 14). 

V. Outer-Sphere Interactions, Association and Self-ionization of Solvents. ... 

It has been mentioned in Section III that [CoCl4] is unstable in water even in the presence of large amounts of alkali metal chlorides. In contrast [CoCl4] is quantitatively formed in concentrated aqueous solutions of hydrochloric acid (66). Outer-sphere interactions between water molecules and hydronium ions will lead to the formation of highly aggregated clusters [H(H20) ]. In this way the concentration of free... 

Outer sphere interactions of this kind are particularly important in the case of strongly polar molecules or charged species. Simulating such effects by a polarizable solvent continuum, DFT... 

STEREOCHEMISTRY, STRUCTURE, AND CRYSTAL ENGINEERING structure and stereochemistry involving lone pair effects, outer sphere interactions, and hydrogen bonding. 

This equation actually describes the interaction between the ion and the first solvation shell. Ions frequently form a very stable "aquo complex with H2O molecules, for example an Fe(H2O)6 complex. Besides this inner sphere interaction there is also an outer sphere one, leading to a corresponding arrangement of the H2O dipoles around the ions. The outer sphere interaction is given by the energy required if an ion with the inner solvation shell (radius /j -1- z-soi) is transferred from a vacuum into the solution, as derived by Born using the continuum model ... 

Because the resonance of limited, nonchelated cu-inositol is very small at high concentrations of Cr , scattered slopes were obtained. Resonances also broadened at higher concentrations of Cr , due to outer-sphere interactions. Sample contained 300 mM Zn (taken from Ref. 30). 

---